A HISTORY OF TOURAINE THROUGH ITS ROCKS
4 - IN CENOMANIAN

Simplified stratigraphical scale (the millions of years (MY) correspond to the period's beginning) :

4500 MY 540 MY 250 MY 65 MY
Eras Precambrian Paleozoic (primary era) Mesozoic (secondary era) Cenozoic (tertiary + quaternary eras)
Periods Triassic Jurassic Cretaceous
Epochs lower Cretaceous upper Cretaceous
96 MY 92 MY 88 MY
Stages Cenomanian Turonian Senonian

The sea returns at the beginning of upper Cretaceous...
The beginning of upper Cretaceous is, at the world level, a period of marine transgression. Touraine, very close to the region where was defined the Cenomanian stage (Le Mans), did not escape from this return of the sea. The big difference with the previous jurassic seas is that, this time, the sea didn't come from east but west, in contact with the very new opening of the north Atlantic Ocean. Previously, Europe and North America formed the same block.

And deposits sands then marls...
The first deposits of Cenomanian are constituted by glauconious sands (the glaucony is a green clayey mineral containing some iron). Today, near to the surface, these green sands become red because of the oxidation of the iron contained in the glaucony. Locally, these sands welded together and became sandstones. Above sands and sandstones, we find some metres of marls with oysters (marls are a mixture of limestone and clay). The totality of the cenomanian deposits represents 50 - 100 m.


      
Sand from Cenomanian - origin: Braslou      Sandstone from Cenomanian - origin: Braslou



Sandstone-like limestone with oysters - origin: Ciran

<<< FROM OXFORDIAN TO LOWER CRETACEOUS IN TURONIAN >>>

The natural context   Touraine's Depths   From Oxfordian to lower Cretaceous   In Cenomanian   In Turonian   In Senonian   In Paleogene   In Neogene   In Quaternary   Map of Indre-et-Loire   Simplified geological map (north)   Simplified geological map (south)

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